The present invention relates to slurry compositions that are useful for polishing or planarizing a surface. The present invention is especially useful for polishing or planarizing copper used as interconnect wiring in integrated circuit devices such as semiconductor wafers containing copper damascene and dual damascene features. The present invention also relates to polishing processes employing the compositions of the present invention.
In the microelectronics industry, during the manufacture of an integrated circuit, surfaces that are typically scratch-free are polished for the purpose of planarizing the structure involved and/or removing unwanted material. The polishing involved is chemical mechanical polishing (CMP). For example, metals such as aluminum, copper, and tungsten are planarized. Moreover, there is typically a refractory metal liner beneath the aluminum, copper or tungsten providing good adhesion to the underlying insulator and good contact resistance to lower level moralizations. Typical liners include niobium, tantalum, tungsten and titanium alone or in combination with their nitrides, oxides and/or oxynitrides or any other refractory metal. Recently copper and alloys of copper have been developed as the chip interconnect/wiring material especially for VLSI and ULSI semiconductor chips.
The use of copper and copper alloys results in improved device performance when compared to aluminum and its alloys.
In fabricating the semiconductor devices, the metallic interconnect material of wiring structure such as copper or its alloys typically starts as a blanket electrodeposited film over a layer of dielectric which has trenched features etched into its surface. The deposited copper film fills the pre-etched gaps or trenches in the dielectric, and leaves a metal overabundance on the surface of the wafer which must be removed. Once the metal overabundance has been removed, an inlaid metal wiring structure is left on the surface of the wafer. This process is referred to as the damascene process. In general, the chemical mechanical polishing (CMP) involves a circular/orbital motion of a wafer under a controlled downward pressure with a polishing pad saturated with a conventional polishing slurry. In this manner, removal of the metal overabundance, and replanarization of the wafer surface is accomplished. More recently, polishing pads which are impregnated with suitable abrasive particles are being used for CMP processing. For a more detailed explanation of chemical mechanical polishing, please see U.S. Pat. Nos. 4,671,851, 4,910,155 and 4,944,836, the disclosures of which are incorporated herein by reference.
Polishing slurries used for CMP of metals are typically aqueous suspensions comprised of a metal oxide abrasive such as alumina or silica, organic acids, surfactants, chelates, and a suitable oxidizing agent. The role of the abrasive is to facilitate material removal by mechanical action. The oxidizing agent works to enhance mechanical removal via a dissolution process. Such oxidizing agents employed in commercially-available or proprietary slurries are typically inorganic metal salts such as Fe(NO3)3, or KIO3, ammonium persulfate as well as hydrogen peroxide, present in significant concentrations. Complexing or chelating agents are present to prevent free copper ion buildup in the process slurry, which can lead to pad discoloration and increased oxidizer reactivity. These additives generally improve the polish performance of the CMP slurry.
One concern with current CMP slurries for Cu is that they typically provide polish rates of 200 to 500 angstroms/minutes. For example see U.S. Pat. Nos. 5,954,997, 6,117,775 and 6,126,853. Increasing the mechanical parameters such as downforce such as up to about 6 psi can provide polish rates of 1500-1700 angstroms/minutes. However, even at these rates, relatively long polish times are required to remove 1 to 2 microns of Cu in Back End Of the Line (BEOL) applications. Employing increased downforce is not desirable when polishing is to be performed on patterned wafers since this tends to result in increased dishing of Cu.
It would therefore be desirable to provide a process for polishing of Cu which overcomes the dishing and erosion problems. Moreover, the polishing process should also avoid scratching the copper surface, which is susceptible to scratching because it is relatively soft. Furthermore, the polishing slurry should provide high selectively towards Cu versus any liner material in contact with the Cu.
Further, by way of background, a description of selective polishing and CMP can be found in U.S. Pat. No. 5,676,587 to Landers at al. entitled xe2x80x9cSelective Polish Process for Titanium, Titanium Nitride, Tantalum Nitridexe2x80x9d which is incorporated herein by reference.
The present invention provides slurry compositions having significantly increased polish rates such as at least about 8000-9000 angstroms/minute without the need for a relatively high downforce of 6 psi or more. Accordingly, the present invention provides a significant reduction in polish times. The invention provides a slurry that can operate with low down force resulting in minimization of Cu recess and oxide erosion during CMP.
Moreover, the present invention provides a slurry that provides high selectivity towards Cu versus one of Ta, TaN, Ti, TiN, W, combinations thereof, and other liner materials by a judicious selection of the components of the composition. In particular, the present invention relates to a slurry composition comprising abrasive particles; an oxidizing and chloride ion source and a sulfate ion source.
The present invention also relates to polishing a surface which comprises providing and the surface to be polished the above disclosed slurry; and polishing the surface by contacting it with a polishing pad.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not restrictive.